Tokyo Electric Power Co. (TEPCO) revealed on May 22 that one of its containers for waste liquid remaining after the processing of contaminated water at the Fukushima No. 1 Nuclear Power Plant did not have the necessary holes in its lid for venting out gas.

A total of 305 containers are being used without having been checked for venting holes. TEPCO says it will quickly inspect all of the containers.

The containers hold sludge and other waste liquids containing radioactive materials that remain after contaminated water is put through the Advanced Liquid Processing System (ALPS). The waste produces gasses like hydrogen, so as a safety measure the Nuclear Regulation Authority had asked TEPCO to create the holes.

In early April, containers were found to be leaking radioactive waste liquids through the venting holes. Later in the month, a company in a cooperative relationship with TEPCO was inspecting the containers when it discovered the container without the venting holes. Out of the approximately 1,400 containers, 334 — including ones that are not being used yet — have not yet been checked for venting holes.

TEPCO has speculated that the work to create the holes was skipped over at a factory in the United States.